Apparatus and method for limiting over travel in a probe card assembly

ABSTRACT

Methods and apparatuses for testing semiconductor devices are disclosed. Over travel stops limit over travel of a device to be tested with respect to probes of a probe card assembly. Feedback control techniques are employed to control relative movement of the device and the probe card assembly. A probe card assembly includes flexible base for absorbing excessive over travel of the device to be tested with respect to the probe card assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/321,743, filed Dec. 16, 2002, (now U.S. Pat. No. 7,084,650).

FIELD OF THE INVENTION

The present invention relates to testing semiconductor devices.

BACKGROUND OF THE INVENTION

Individual semiconductor (integrated circuit) devices (dies) aretypically produced by creating several identical devices on asemiconductor wafer using known techniques of photolithography,deposition, diffusion and the like. These processes are intended tocreate a plurality of fully functional integrated circuit devices, afterwhich the individual dies are singulated (severed) from thesemiconductor wafer. In practice, physical defects in the wafer itselfand/or defects in the processing of the wafer often lead to some of thedies being “good” (fully functional) and some of the dies being “bad”(non-fully functional). It is generally desirable to be able to identifywhich of the plurality of dies on the wafer are good dies prior to theirpackaging (encapsulation within a transfer-molded plastic, ceramic ormetal package for subsequent integration into a circuit), and preferablyprior to their being singulated from the wafer. To this end, a wafertester or “prober” is used to make a plurality of discrete pressureconnections to a like plurality of discrete connection pins (or bondpads) on the dies. In this manner, the semiconductor dies can be testedand exercised prior to singulating the dies from the wafer. Aconventional component of a wafer tester is a probe card assembly. Inuse, the wafer or device under test (DUT) and the probe card assemblyare brought together so that the outboard tips of a plurality of probeelements are brought into electrical engagement with corresponding diepads on the wafer.

SUMMARY OF THE INVENTION

The present invention relates generally to testing semiconductordevices. In one aspect, the invention relates to over travel stops forlimiting over travel of a device to be tested with respect to probes ofa probe card assembly. Other aspects of the invention include feedbackcontrol of relative movement of the device and the probe card assemblyand a probe card assembly with a flexible base for absorbing excessiveover travel of the device with respect to the probe card assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, partially cross-sectional, partially diagrammatic viewof a semiconductor tester 5 with probe card assembly 10 positioned toengage with a semiconductor device 11 (“DUT”) in accordance with anexemplary embodiment of the present invention.

FIG. 2 is a side, partially cross-sectional view of the probe cardassembly 10 of FIG. 1 shown in engagement with DUT 11.

FIGS. 3 a-3 f are side, cross-sectional views showing, in stages, thefabrication of probe tips 21 and stop plates 23.

FIGS. 4 a-4 c are side, partially cross-sectional views showing, instages, fabrication and assembly of space transformer assembly 40.

FIG. 5 is a bottom view of the probe card assembly 10 of FIG. 1.

FIG. 6 is a side, partially cross-sectional view of a probe cardassembly 45 positioned to engage with a semiconductor device 11 (“DUT”)in accordance with an alternative embodiment of the present invention.

FIG. 7 is a side, partially cross-sectional view of the probe cardassembly 45 of FIG. 6 shown in engagement with DUT 11.

FIG. 8 is a side, cross-sectional and partially diagrammatic view of aprobe card assembly 56 in accordance with another embodiment of thepresent invention.

FIG. 9 is a plan, diagrammatic view of the probe card assembly 56 ofFIG. 8.

FIG. 10 is a side, cross-sectional view of a portion of probe cardassembly 56 of FIG. 8 and positioned to engage with a wafer 71.

FIG. 11 is a side, cross-sectional view of the probe card assembly 56 ofFIG. 10 and shown in engagement with wafer 71.

FIG. 12 illustrates an exemplary microprocessor based controller.

FIGS. 13 and 14 illustrate exemplary processes for controlling movementof a wafer into contact with a probe assembly.

FIGS. 15 a-15 c illustrate a probe card assembly with a flexible base.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiments illustrated inthe drawings and specific language will be used to describe the same. Itwill nevertheless be understood that no limitation of the scope of theinvention is thereby intended, and any alterations or modifications inthe illustrated device, and any further applications of the principlesof the invention as illustrated therein are contemplated as wouldnormally occur to one skilled in the art to which the invention relates.

Referring to FIG. 1, there is shown a semiconductor tester 5 for testingsemiconductor devices. Tester 5 generally includes a probe card assembly10, support structure 12, control apparatus 13 and a semiconductordevice holder 18. Probe card assembly 10 is shown positioned to engagewith and test a semiconductor device 11 (otherwise known as a deviceunder test or “DUT”) in accordance with the present invention.

The exemplary probe card assembly 10 illustrated in FIG. 1 generallyincludes a base assembly 14, a space transformer 15, a plurality ofprobes 16 (eight of many shown), and a plurality of overtravel stopassemblies 17. Support structure 12 supports probe card assembly 10 andcan be operable to move probe card assembly 10 toward DUT 11 or to holdprobe card assembly 10 stationary while DUT 11 is moved toward probecard assembly 10. Holder 18 is connected with support structure 12 andis configured to hold DUT 11 stationary during the testing procedurewhile probe card assembly 10 is moved toward DUT 11 or to move DUT 11toward probe card assembly 10. Semiconductor device holder 18 can be inany configuration that securely holds semiconductor device 11 duringtesting. Holder 18 may also be configured to grasp a semiconductordevice 11 from an indexing unit, move it into testing position, hold itand/or move it during testing, and then move it out of tester 5 to anoutput station. Holder 18 is contemplated in one embodiment to includeelectronic connection apparatus for electronically connecting orfacilitating such connection of semiconductor device 11 with controlapparatus 13. Control apparatus 13 is connected with support structure12 and DUT holder 18 and includes elements such as computer hardware andsoftware for controlling movement of probe card assembly 10 and/or DUT11. In alternative embodiments, control apparatus 13 does not rely oncomputer components to control movement of probe card assembly 10 and/orDUT 11, but instead provides any type of manual actuation apparatusincluding, but not limited to levers, linkages, a rack and pinionmechanism, cables, pulleys and/or similar devices for moving probe cardassembly 10 and/or DUT 11. Control apparatus 13 is also electronicallyconnected with probe card assembly 10 and connectable to DUT 11 (eitherindividually or through holder 18) to send and receive data testingsignals thereto and therefrom.

Although probe card assembly 10 is illustrated in FIG. 1 as comprising abase 14 and a space transformer 15, probe card assembly may be any typeof probe card assembly. For example, probe card assembly 10 may be assimple as only a base 14 to which probes 16 and over travel stops 17 aredirectly attached. As another example, probe card assembly 10 maycomprise a more complex assembly of parts, such as the probe cardassembly illustrated in U.S. Pat. No. 5,974,662, which is incorporatedby reference herein in its entirety. Probes 16 may be any type ofprobes, including without limitation needle probes, buckling beam probes(e.g., “COBRA” probes), bumps, posts, and spring probes. Nonexclusiveexamples of spring probes include the spring contacts described in U.S.Patent Application Publication 2002/0055282 A1, U.S. patent applicationSer. No. 09/032,473 (filed Feb. 26, 1998), U.S. patent application Ser.No. 10/262,712 (filed Jul. 24, 2002), U.S. Pat. Nos. 6,268,015, and5,917,707, all of which are incorporated by reference in their entiretyherein.

DUT 11 is a semiconductor wafer on which have been fabricated aplurality of integrated circuit chips or “dice” (not shown). Eachindividual die has a number of pins or bond pads 19 for providing power,ground, and signals such as data, address, control, etc. to the die. DUT11 may contain many hundreds of bond pads 19 disposed in close proximityto one another (e.g. 5 mils center-to-center), and the bond pads may bearranged in configurations other than a single row near the edge of thedie. Because of the close proximity of many bond pad arrays, the tips ofprobes 16 may often need to be spaced more closely to one another(relatively fine pitch) than the connections to their base assembly 14.“Space transforming” (sometimes referred to as “pitch spreading”) maytherefore be incorporated in the present application by a spacetransformer, representatively shown at 15 (comparable to element 506 inthe U.S. Pat. No. 5,974,662 patent). Space transformer 15 facilitatesmaking a reliable testing connection between the plurality of probes 16and the corresponding bond pads 19 of DUT 11 by redirecting spatiallyindiscriminate input connections (not shown) from base assembly 14 to aspecifically organized array of probes 16 that align with the matingarray of bond pads 19 as shown, for example, in FIG. 1. The inputconnections (not shown) from base assembly 14 to space transformer 15may be formed in any suitable manner.

Each of the exemplary plurality of probes 16 includes a resilientinterconnecting wire element 20 and a probe tip 21. Each exemplary overtravel stop assembly 17 includes a pair of substantially rigid posts 22and a stop plates 23. Each post 22 is rigidly mounted in any suitablemanner at one end to space transformer 15, and at its opposing end ismounted to a stop plate 23. As DUT 11 and probe card assembly 10 arebrought together and probe tips 21 engage with corresponding bond pads19, the resilient, spring-like wire elements 20 deform (as shown in FIG.2). The neighboring over travel stop assemblies 17 engage DUT 11 at apredetermined distance (a proximity limit) to physically limit how closeDUT 11 and probe card assembly 10 can get, and consequently to ensurethe proper pressure engagement between probe tips 21 and bond pads 19.

Referring to FIGS. 3 a-3 g and 4 a-4 c, there is shown an exemplarymethod for making a portion of probe card assembly 10 in accordance withone embodiment of the present invention. As shown in FIG. 3 a, aplurality of pits 26 are etched in a sacrificial substrate 27, such as asemiconductor wafer, using known methods such as masking. The number andarrangement of pits 26 correspond to the number and arrangement of bondpads on the corresponding DUT to be tested. These pits 26 will form theends 28 of probe tips 21. Referring to FIG. 3 b, an optional first masklayer (mask 31) is formed, using known methods, over sacrificialsubstrate 27, proximal to pits 26, and in a specific size and shape.Mask 31 is preferably a photoresist material, such as SU8.

Referring to FIG. 3 c, a release (and/or seed) material 32 is formedover the substrate and mask 31. Release material 32 is applied tofacilitate separation between sacrificial substrate 27 and mask 31thereunder and the probe tips 21 and stop plates 23 formed on topthereof. Also, if the probe tips 21 and stop plates 23 are formed byelectroplating, release material 32 will provide the conductive layernecessary for electroplating. In one embodiment, release material 32comprises aluminum. Other appropriate materials may be used for releasematerial 32 including, but without limitation, copper, titanium,tungsten or alloys of these and/or other materials including materialsmade of two or more layers of such materials that function as describedabove. For purposes of illustration, the dimensions of certain elementsshown in the figures may be exaggerated or not in proportion.

Referring to FIG. 3 d, a second mask layer (mask 33) is formed in aspecific pattern over sacrificial substrate 27, mask 31 and releasematerial 32, as shown. Mask 33 defines a plurality of cavities 35 and 36that are sized and shaped to create probe tips 21 and stop plates 23,respectively. A preferably conductive material is then deposited intocavities 35 and 36 to form probe tips 21 and stop plates 23, as shown inFIG. 3 e. The material used to form tips 21 and plates 23 is generallydesired to be conductive, non-oxidizing, and chemically non-reactive.Examples of appropriate materials include, without limitation,palladium, gold, rhodium, nickel, cobalt, silver, platinum, conductivenitrides, conductive carbides, tungsten, titanium, molybdenum, rhenium,indium, osmium, rhodium, copper, refractory metals, and their alloys aswell as alloys of these and/or other materials. Any appropriate methodmay be used to deposit such material into cavities 35 and 36 such as,but without limitation, chemical vapor deposition, physical vapordeposition, sputtering, electroless plating, electron beam deposition,and thermal evaporation. Alternatively, a non-conductive material may beused for either or both of probe tips 21 and stop plates 23 such asaluminum oxide, aluminum nitride, etc. In the event a non-conductivematerial is used for probe tips 21, at least the ends 28 of tips 21 mustbe made conductive and must be electrically connected to wire elements20. This may be done in any suitable manner such as, and withoutlimitation, by coating the exterior surface of probe tips 21 with aconductive material. After formation of probe tips 21 and stop plates23, mask 33 is removed to expose the probe tips 21 and stop plate 23, asshown in FIG. 3 f. Because the tips 21 and stop plates 23 are formedlithographically, they may be formed with relatively precise spatialrelationships to each other.

Referring to FIG. 4 c, the assembly 36 of probe tips 21 and stop plates23 of FIG. 3 f are shown having been connected to space transformer 15.More specifically, interconnecting wire elements 20 connect probe tips21 to space transformer 15 to form the plurality of probes 16, and stopplates 23 are connected to and a fixed distance from space transformer15 by posts 22 to form over travel stop assemblies 17. In oneembodiment, such wire elements are formed and connected to spacetransformer 15 using the wire bond technique wherein each wire is madeof a relatively soft, malleable material and is bonded in a knownmanner, at the desired location, to space transformer 15 (FIG. 4 a).Posts 22 may be formed in like manner, but may be thicker to be rigidand/or made of a material that is more rigid. The wire may then beovercoated with a harder, resilient material. Exemplary descriptions ofthis technique are provided in U.S. Pat. Nos. 5,476,211, 5,917,707, and6,336,269, which are hereby incorporated by reference.

Alternatively, elements 20 need not be wires. For example, elements 20may be resilient spring-like structures formed lithographically byapplying and patterning a masking layer to space transformer 15 and thendepositing material in the openings in the masking layer or layers asgenerally illustrated in FIGS. 3 b and 3 e above. Indeed, elements 20may be fashioned in a variety of shapes by molding the masking layer(s)to have the negative of the desired shape (an example of this techniqueis as described in U.S. Patent Application Publication 2002/0055282 A1,which is incorporated in its entirety herein by reference) or by usingmultiple masking layers with different patterned openings to define thenegative of the desired shape of elements 20 (an examples of thistechnique are described in U.S. patent application Ser. No. 09/032,473(filed Feb. 26, 1998) and U.S. Pat. No. 6,268,015, both of which arealso incorporated in their entirety herein by reference). Alternatively,such lithographic techniques may be used to build elements 20 over thetips 21 and posts 22 over stop plates 23 following the step illustratedin FIG. 3 e. All of the foregoing techniques may also be used to makeposts 22.

As should be apparent from the foregoing, the invention is not limitedto any particular type of probe. Rather, the present inventioncontemplates use of any appropriate probe including, without limitation,needle probes, buckling beam probes (e.g., “COBRA” probes), bumps,posts, and spring probes, examples of which are discussed above.Moreover, the probes may be made and assembled into an array in anymanner. For example, probes may be made lithographically, by machining,by stamping, by molding, by microelectrical mechanical system (MEMS)processes, etc. and then assembled into an array. An example in whichprobes are made using a MEMS process and then assembled into an array isdiscussed in U.S. patent application Ser. No. 10/262,712 (filed Jul. 24,2002), which is incorporated in its entirety herein by reference.

The stop structures may also be made and assembled in of the foregoingways. Typically, posts 22 are made with sufficient rigidity that, uponengagement of over travel stop assemblies 17 with DUT 11, posts 22 willnot significantly deform and will physically stop further travel of DUT11 toward probe card assembly 10.

Referring again to the example illustrated in FIGS. 3 a-4 b, as shown inFIG. 4 b, the assembly 38 (FIG. 4 a) of wire elements 20 and posts 22extending from space transformer 15 is then brought together with theassembly 36 (FIG. 3 f) of probe tips 21 and stop plates 23 formed uponon sacrificial substrate 27. As shown, probe tips 21 and stop plates 23are all sized and located on sacrificial substrate 27, and wire elements20 and posts 22 are all sized and located on space transformer 15, sothat each probe tip 21 aligns with a corresponding wire element 20 andeach stop plate 23 aligns with a corresponding pair of posts 22. Probetips 21 are then permanently bonded to wire elements 20, and stop plates23 are permanently bonded to posts 22. Such bonding may be performed inany appropriate manner such as, and without limitation, soldering orbrazing. Such connection methods are described with reference to FIGS.8D and 8E in the U.S. Pat. No. 5,974,662 patent.

Following connection of the probe tips 21 and stop plates 23 to wireelements 20 and posts 22, respectively, sacrificial substrate 27 isremoved by any appropriate method such as, but without limitation,etching or dissolving. The resulting space transformer assembly 40 maybe joined with other components to form a probe card assembly 10, suchas the probe card assembly shown in FIG. 5 of the U.S. Pat. No.5,974,662 patent.

In use, when DUT 11 and probe card assembly 10 are brought together andprobe tips 21 engage with corresponding bond pads 19, the resilient,spring-like wire elements compress or deform (as shown in FIG. 2). Toensure that DUT 11 moves close enough to probe card assembly 10 to allowall of probes 16 to deform and achieve a sufficiently resistive springforce and thus reliable pressure contact with their corresponding bondpads 19, neighboring over travel stop assemblies 17 engage DUT 11 at apredetermined distance of travel to physically preclude additional overtravel. With probe card assembly 10 constructed as described and shownin FIG. 1, the combined depth of pits 26 and the thickness of mask 31corresponds to the over travel distance 41 (FIG. 1) permitted by thepresent invention.

The probe card assembly 10 of FIG. 1 shows just eight probes 16 and apair of neighboring stop assemblies 17. Another configuration is shownin FIG. 5 where the probe card assembly 42 (bottom view) has two arrays43 and 44, each containing 48 probes 16 extending downwardly from spacetransformer 15, and where there are six over travel stop assemblies 17spaced around the outside of the two arrays 43 and 44. It iscontemplated that probe card assembly 42 or a similar probe cardassembly may be used to test DUT's with fewer bond pads 19 than arecontained in the corresponding array(s) of probes 16. Such excess probes16 that do not contact a corresponding bond pad (or an inactive bondpad) can be deselected by software.

The test system in which the probe card assembly of the presentinvention is incorporated may operate to move DUT 11 toward a stationaryprobe card assembly 10 or to move probe card assembly 10 toward astationary DUT 11 or to move both DUT 11 and probe card assembly 10towards each other. Further, such test system may be configured for suchmovement by the DUT 11 and/or probe card assembly 10 to be effectedmanually or automatically. It is contemplated that such test system willincorporate any appropriate configuration of machinery, computerhardware and software to effect such manual or automatic movement, toprovide for adjustment of the limits, path and rate of such movement,and to receive, process and display output data produced during suchmovement and from the engagement between the DUT and the probe cardassembly.

Alternative embodiments are contemplated wherein there are more or lessthan two posts 22 connecting and holding each stop plate 23. Alternativeembodiments are contemplated wherein plates 23 are in shapes other thanthe relatively planar and rectangular configuration shown. Alternativeembodiments are contemplated wherein posts 22 are not rigid, but insteadare somewhat resilient to provide a degree of “give” or “compliance”when DUT 11 engages with over travel stop assemblies 17. For example, asshown in FIG. 6, a probe card assembly 45 is shown in accordance withanother embodiment of the present invention wherein the stop plates 46and 47 of over travel stop assemblies 48 and 49 are held by resilientposts 50. (Like probe card assembly 10 of FIG. 1, the probe cardassembly 45 shows just eight probes 16 and just two over travel stopassemblies 48 and 49. The invention contemplates any number of probesand stop assemblies to properly engage with the bond pads of a DUT 11 tobe tested). Posts 50 may be formed and connected to space transformer 15using any appropriate method, including those techniques discussedherein for forming and connecting wire elements 20.

One benefit of making posts 50 resilient is realized in the event thatDUT 11 is at all non-planar, that any of stop plates 46 and 47 are orhave become non-planar, that stop plates 46 and 47 of over travel stopassemblies 48 and 49 are or have become mutually non-planar, and/or thatDUT 11 is not parallel to the plane of the stop plates 46 and 47 at themoment of engagement therewith. Thus, referring to FIG. 7 where, inexaggerated fashion, DUT 11 is shown to be non-planar at the moment ofinitial engagement, the resiliency of posts 50 allows the first stopplate 46 to engage, and its resilient posts will deform until the otherstop plate 47 likewise engages. The resiliency of posts 50 is selectedto permit such deformation by one or a few of the posts when necessary,but to also still provide a physical over travel limit when all the overtravel stop assemblies 48 are engaged. Alternative embodiments arecontemplated where posts 50 are made to be both rigid and resilient.That is, a portion of each post 50 is made resilient to enable a limiteddegree of give (as shown in FIG. 7) and another portion of each post ismade rigid to define the maximum limit of give, and thus overtravel.Alternative embodiments are also contemplated wherein plates 23 are notrigid, but instead are somewhat resilient to provide a degree of “give”or “compliance” when DUT 11 engages with over travel stop assemblies 17.

Alternative embodiments are contemplated wherein one or more over travelstop assemblies are wired to provide a signal that the corresponding DUT11 has been engaged. Such signal may simply indicate engagement or maysignal the extent of engagement (e.g., by signaling a degree of forceexerted by the wafer on the probes or the over travel stop). Forexample, such signal may provide a binary output x: no contact (x=0),contact (x=1). Alternatively, a more detailed response may be providedby the output value x: no contact (x=0), contact (0<x≦1) where any xgreater than 0 indicates contact and the value of x greater than 0 andless than or equal to 1 indicates the extent of travel of the DUT frominitial contact up to and including the limit of travel. Such outputsignal is contemplated to be received as input by computer componentsconnected with the probe card assembly and displayed in any appropriateform and/or used to further control the overall probe testing operation.Typically, such output signal would be sent to the tester or prober,which would then stop movement of the probe card assembly toward thesemiconductor wafer when the desired over travel limit is reached.

An example of such assembly in shown in FIG. 8, where a probe cardassembly 56 includes over travel stop assemblies 57 that are wired toprovide over travel position output signals. Like probe card assembly 45of FIG. 6 and similar to the probe card assembly 500 of FIG. 5 of theU.S. Pat. No. 5,974,662 patent, probe card assembly 56 includes an array58 of probes 59 and over travel stop assemblies 57 mounted to a spacedtransformer 61, which is electronically connected by variousinterconnection wire elements 62 and an interposer 63 to a probe cardassembly 65. An over travel control unit 66 is wired to the over travelstop assemblies 57 whereby the over travel output signals aretransmitted to control unit 66, which transmits corresponding signals tothe tester/prober (not shown). The allowable over travel is indicated at67. FIG. 9 is a plan view of the probe card assembly 56 showingdiagrammatically one exemplary placement of over travel stop assemblies57 relative to the array 58 of probes 59.

FIGS. 10 and 11 illustrate one exemplary arrangement for detectingcompletion of a desired amount of over travel of bond pads or pins 73,74 of wafer 71 with respect to probes 59. Referring to FIG. 10, the overtravel stop assemblies 57 are arranged in adjacent pairs. Thus, at eachof the four sites of the probe card assembly 56 of this embodiment (FIG.9), probe card assembly 56 includes a pair of over travel stopassemblies 69 and 70. In each die on the wafer 71 to be tested, the bondpads or pins 73, 74 comprise functioning pins 73 and dummy pins 74.(Pins 73, 74 in FIGS. 10 and 11 are shown as having slightly differentheights due to inherent manufacturing imprecision.) Functioning pins 73are functional in providing the desired power, ground and signalcapabilities for their corresponding die 76 (or 77), while dummy pins 72are shorted to ground.

In use, when wafer 71 and probe card assembly 56 are brought together,probe tips 59 will engage with corresponding pins on the DUT 11 (deviceunder test) 78. Because of the resiliency of the wire element 80 of eachprobe 59, each probe 59 will deform as necessary and engage with each ofits corresponding pins 73 and 74. It should be noted that there may ormay not be a probe 59 that corresponds to a particular dummy pin 74. Itshould also be noted that the contact plates of over travel assemblies69 and 70 are preferably made to correspond to known locations of dummypins 74 on wafer 71. A circuit will be completed and a correspondingsignal will be generated and transmitted through control unit 66 to theprober/tester (not shown), and movement of probe card assembly 56 towardwafer 71 will stop. The invention contemplates that the system softwarewill be configured to control the testing operation in response to anydesired contact combination. That is, in one embodiment, contact by anytwo adjacent over travel stop assemblies (i.e. 69 and 70) with dummypins will cause movement of probe card assembly 56 to stop.Alternatively, referring to FIGS. 8 and 9, any one over travel stopassembly (i.e. 69) at one side 81 of array 58 and any one over travelstop assembly (i.e. 82) at another side 83 (or 84 or 85), can beprogrammed to stop movement of probe card assembly 56. Alternatively,just one over travel stop assembly (i.e. 69) could be programmed to stopmovement of probe card assembly 56.

Alternative embodiments are contemplated wherein two or more over travelstop assemblies are wired as above and the output thus indicates whichover travel stop assemblies have engaged with the DUT 11 and by howmuch. Such output, from just one or from a plurality of the over travelstop assemblies, is contemplated to be made available for display orother recognition by a human or machine. Thus, such output may simply beindicated by a single LED flashing or by a buzzer. Alternatively or inaddition, a display screen may diagrammatically indicate the entireprobe card assembly layout and show by any appropriate display whichover travel stop assemblies have been engaged and by how much.Alternatively or in addition, the output signal may be received by acomputer or other machine and acted upon. For example, a signal that anover travel stop assembly has engaged a bond pad or pin may cause thesystem to cease movement of the probe card assembly toward the DUT 11,or visa versa, or movement for only another pre-programmed distance.Where the output signal indicates the extent of engagement, suchinformation can be used by the human user or the machine to adjust thelimits of movement of the DUT relative to the probe card assembly, aswell as the rate of such movement.

FIGS. 13 and 14 illustrate exemplary methods for automaticallycontrolling movement of a wafer to be tested into contact with a probecard assembly, and FIG. 12 illustrates a feedback controller 530 thatmay implement any of the processes of FIGS. 13 and 14. The exemplaryfeedback controller 530 illustrated in FIG. 12 is a microprocessor basedcontroller and may be, for example, part of control apparatus 13. Asshown, it includes a digital memory 532, a microprocessor 534, and aninput/output port 536. Input data 538 is received and output data 540 isoutput through input/output port 536. The digital memory 532 may be anytype of memory including an electronic memory, an optical memory, amagnetic memory, or some combination of the foregoing. As just twoexamples, digital memory 532 may be a read only memory, or digitalmemory 532 may be a combination of a magnetic or optical disk and arandom access memory. Microprocessor 534 executes instructions (whichmay be in the form of software or microcode) stored in digital memory532.

The exemplary methods illustrated in FIGS. 13 and 14, which may beimplemented in software and executed on a microprocessor based systemsuch as the one illustrated in FIG. 12, will be explained with referenceto a probe card assembly 56 such as the one illustrated in FIGS. 8-11 ina tester 5 like the one illustrated in FIG. 1. For purposes ofdiscussion only, it is assumed that a wafer such as exemplary wafer 71is moved while probe card assembly 56 is held stationary. Of course, thewafer could alternatively be held stationary and probe card assemblymoved, or both the wafer and the probe card assembly could be moved. Thewafer 71 may be supported by any appropriate means, such as the waferholder 18 illustrated in FIG. 1, which itself is moved by anyappropriate means, such as an electric motor (not shown). Output data540 (FIG. 12) includes signals that control movement of the wafer 71(e.g., by moving the wafer holder 18), and input data 538 includessignals from over travel control unit 66 or other sensors (e.g., theoutput of over travel control unit 66 may be directed to feedbackcontroller 530 as input data 538).

The exemplary method illustrated in FIG. 13 utilizes one or more sensorsfor detecting when the wafer 71 has been moved into contact with theprobes 71 and then further moved by a desired amount of over travel pastfirst contact. For illustration purposes, the sensor(s) is assumed tocomprise over travel stop assemblies 69, 70 wired to detect contact asillustrated in FIGS. 10 and 11. It should be understood, however, thatany sensor for detecting or estimating when the wafer 71 has been movedthe desired over travel distance may be used. Such sensors include byway of example acoustic sensors, optical sensors, etc., which may beused to detect, for example, when the over travel stops reach aparticular position. It should also be noted that one to several suchsensors may be used, and if a plurality of sensors are used, the sensorsmay be arranged in any pattern on probe card assembly 56. The pattern offour sensors 81, 83, 84, 85 illustrated in FIG. 9 is but one exemplarypattern.

Turning now to the exemplary method illustrated in FIG. 13, thisexemplary method begins after wafer (e.g., wafer 71 shown in FIGS. 10and 11) has been placed on a moveable holder (e.g., wafer holder 18illustrated in FIG. 1), and pads or pins 73, 74 of wafer have beenaligned with probes 59, as illustrated in FIG. 10. As shown in FIG. 13,the first step 110 is to move the wafer 71 toward the probe cardassembly 56. At step 112, it is determined whether the pins 73, 74 onwafer 71 have been moved into contact with probes 59 and over traveledthe desired distance. If no, movement of the wafer 71 toward the probecard assembly 56 continues (step 110). If yes, movement of the wafer 71is stopped at step 114.

Determining whether pins 73, 74 have reached the desired over-travel(step 112) may be detected or estimated in any way. As just one example,stop structures 69, 70, such as those illustrated in FIGS. 10 and 11 maybe configured so that an over travel sensor 66 generates a signal whenover travel stops 69, 70 contact pins 73, 74. That signal may be inputto controller 530 as input signal 538. As mentioned above, other typesof sensors may be used. Also, any number of sensors may be used, and ifmultiple sensors are used, they may be positioned in any suitablepattern. If multiple sensors are used, a signal indicating that thedesired amount of over travel has been reached may be triggered by anyone or more of the sensors in any desired pairing or sequence. Forexample, referring to the exemplary pattern of sensors 81, 83, 84, 85shown in FIG. 9, a over-travel-reached state may be found to beaffirmative at step 112 when any one of the sensors 81, 83, 84, 85 isactivated. As another nonexclusive example, the over-travel-reachedstate may be found to be affirmative at step 112 only after all foursensors 81, 83, 84, 85 are activated. As another example, theover-travel-reached state may be found at step 112 after a pair ofsensors (e.g., opposite pairs 81, 83, or pairs 84, 85) are activated.Many other combinations are possible.

Turning now to the exemplary method illustrated in FIG. 14, thisexemplary method also begins after a wafer (e.g., wafer 71 shown inFIGS. 10 and 11) has been placed on a moveable holder (e.g., waferholder 18 illustrated in FIG. 1), and pads or pins 73, 74 of wafer 71have been aligned with probes 59, as illustrated in FIG. 10. As shown inFIG. 14, the first step 202 is to move the wafer 71 toward the probecard assembly 56 at an initial speed. During this movement, the forcethe wafer pads or pins 73, 74 exert against probes 59 is determined atstep 204, and it is determined at step 206 whether the force exceeds apredetermined maximum force. (Of course, before first contact betweenthe pads or pins 73, 74 and probes 59, the force is zero.) If yes,movement of the wafer 71 toward the probe card assembly 56 is stopped atstep 210 (e.g., controller 530 issues control signals 540 that causemovement to stop). If, however, the determined force is less than themaximum force (step 206), at step 206, the speed of the movement of thewafer 71 toward the probe card assembly 56 is adjusted in accordancewith the force determined at step 204 (e.g., again the controller 530issues control signal(s) 540 that adjusts the speed). Preferably, thespeed is decreased as the force increases. The steps of moving the wafer71 toward the probe card assembly 56 (step 202), determining the force204, and adjusting the speed of the wafer 71 (step 208) are repeateduntil the force on the probes 56 exceeds the maximum force (step 206).It should be noted that step 208 is optional. That is, the process ofFIG. 15 can be performed without adjusting the speed following anegative determination at step 206.

Again, there are many different types of sensors that may be used todetermine or estimate the force on a probe. For example, over travelstops 69, 70 may be fitted with force measuring sensors (e.g., apiezoelectric material). Alternatively, force measuring device(s) may beconnected directly to one or more probes 59. Also, one or more suchsensors may be used. If more than one is used, the step of determiningthe force 204 may comprise averaging the forces detected by all of thesensors.

FIGS. 15 a-15 c illustrate a probe card assembly 446 in which base 414is made of a flexible material. As will be seen, because the base 414 isflexible, it absorbs extra over travel, As shown in FIG. 15 a, waferholder 18 brings wafer 11 into first contact with probes 16. As shown inFIG. 15 b, wafer holder 18 moves wafer 11 past the point of firstcontact by an over travel distance 41. As shown in FIG. 15 c, forwhatever reason, wafer holder 18 moves wafer 11 beyond the desired overtravel 41 by an additional over travel distance 441. Normally, theadditional over travel 441 could cause excessive forces to be exerted onthe over travel assemblies 17 and possibly the probes 16. As also shownin FIG. 16 c, however, the base flexes, absorbing all or at least partof the additional over travel 441, eliminating or at least reducing theexcessive forces caused by the additional over travel 441. The base 414may be made of any material that is sufficiently rigid to support probes16 but sufficiently flexible to absorb all or part of over travel 441.Examples of such materials include, without limitation, printed circuitboard material, Mylar, organic materials, rubbers, and plastics.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the same is to be considered asillustrated and not restrictive in character, it being understood thatonly the preferred embodiment has been shown and described and that allchanges and modifications that come within the spirit of the inventionare desired to be protected.

1. A method of making a probe card assembly, said method comprising:forming a plurality of probes on a surface of a substrate; and forming astop structure on said surface of said substrate, wherein said forming aplurality of probes and said forming a stop structure comprise:lithographically forming a plurality of tip structures and a stop plateon a sacrificial substrate; and transferring said tip structures to aplurality of probe bodies attached to said surface of said substrate;and transferring said stop plate to a stop support attached to saidsurface of said substrate.
 2. The method of claim 1, wherein: saidtransferring said tip structures to a plurality of probe bodies attachedto said surface of said substrate, and said transferring said stop plateto a stop support attached to said surface of said substrate comprise:attaching said tip structures to said probe bodies; attaching said stopplate to said stop support; and releasing said tip structures and saidstop plate from said sacrificial substrate.
 3. The method of claim 1,wherein said lithographically forming a plurality of tip structures anda stop plate on a sacrificial substrate comprises: patterning aplurality of masking layers; and depositing material within saidpatterned masking layers to form said tip structures and said stopplate.
 4. The method of claim 3, wherein said patterned masking layersdefine shapes of said tip structures and said stop plate.
 5. The methodof claim 3, wherein said patterned masking layers define relativelocations of said tip structures and said stop plate.
 6. The method ofclaim 5, wherein contact portions of said tip structures are located ina first plane and a contact portion of said stop plate is located in asecond plane, and said first plane is a predetermined distance from saidsecond plane.